Vapor rectifier



Filed Feb. 13, 1928 Patented Aug. 30, 1932 vas ems; STATES ARTHUR GAUDENZI, or impa r, SWITZERLAND, rissreuoit {no AKT IE NGESELLSGI-IAET BROWN BOVEBI a 01s., or BADEN, SWITZERLAND, A JomT-sTocK company or SWITZERLAND VAPOR RECTIFIER.

Application filed February 13,: 1928, Serial K0. 253,943, and iii-Germany May. 13, 1927.

This invention relates toI-electric power rectifiers of the mercury vapor type, andfinds particular utility in its application to metal tank polyphase rectifiers such asfidescribed in the Bulletin of-the Brown Boveri Company of Baden, Switzerland, entitled Brown- Boveri mercury arcrectifiers for large outputs published July, 1926.

- The'general object of tne invention is the provisio'nof an improved construction and an nnproved method for operating rectifiers of this type, which construction and method are adapted to preventbackfiring or reversals of the current flow in the rectifier or in the several anodes thereof.

Other objects are the provisionjof such a construction and method of operation which are simple and reliable. V l

Still other objects will be pointed out or indicated hereinafter or will become apparent to one skilled in the art upon employment of the invention in practice.

In the drawing forming a part of this specification I illustrate diagrammatically various structural arrangements in which the invention may be embodied or by use of which it may be practiced, but it is to be understood that these are presented for the purpose of illustration only and that they are not to be accorded any interpretation having the effect of limiting the claimsshort of the true and most comprehensive scope ofthe invention in the art.

Insaiddrawing, Fig. 1 is a schematic illustrationin the nature of a sectional elevationof a rectifier, illustrating the essential features of one arrangement of apparatus. embodying the invention but omitting various parts of the rectifier itself. T

Fig. Qis a similar illustration but'showing I a different arrangement of the features of by the present invention;

the present invention.

Fig. 3 is a similar illustration representing two other forms of apparatus comprehended Fig. 4 is a cross-section detail on line 44 of Fig. 3. I v

y In ,the'operation of mercury-vapor rectifiers, there is alternately applied to each anode a positive and anegative voltage, the

anodes permitting current. to flowto the oathvalveactioh of the anodes, on; whichthe operationof the'rectifier is. based, presents 7 one of the greatest diflicultiesin the .develop ment of satisfactory and practical power .rectifiers. Very often an anode loses the check valve action at the moment when it is negative, resulting in a current reversal or backfire, that is ,-a short-circuit current flow from the active positive anodes to the temporarily inactive negativeanode. l q I have conducted extens ve experlmentation for the-purpose of determining the factors or conditions which contribute to reverse arcing, andhave ascertained that reverse arcing. is more likely to occurif there isia concentration of mercury vapor or gas in the neighborhood of the anodes. The arca'tthe mercury surface produces strong l eva'porization of mercury, and asla result,'there is a tremendous blast Ofmer'cury vap or, continuously passing fromthecathodeto the :cooled walls of the tank. This blast must be kept away from the anodes. 'Butit is not sufficient simply to divert the rising stream of mercury vapor away from the}anodes,'-asthe-expansion oftheniercury vapor fills the entire casing with it and tends to produce "an excessive density of the gas and vapor about the anodes. The present invention provides, in addition to the diverting of the mercury} vapor from the anodes, for the reduction of theVa por density in the region of the anodesby main- ,taining there a temperature properly in ex- 7 cess ofwhat would be thenormaltemperature of the vapor in those localities. The' heatin'g maybe confined principallyto the: spaces enclosed by the anode shields, and may be effected by suitableheat-generating or heatmaintaining elements which are supplied either by the rectifier current or from a sep: arate source.

Examples of isuclrheating arrangements .for the anodespace are illustrated in the drawing, wherein the. reference numeral. 10

the shields are soarranged away from the center of the rectifier thatthe vaporblastis .diverted from the anodes and mercury particles prevented from impingement upon'the' anodes, in the well known manner as. found for instance, in the present Brown Boveri rectifiers described in the Bulletin ,of 1926,

referred to before. In order, to reduce the :possibility'of backfire, special heating means 'are provided in the rectifier for decreasing the density of the vapor in the region adjacent to the anodes. In the example shown in Fig. 1 heating elements 15, in the form of coils of resistance wire, are disposed within the shields, being insulated from them, if they are metal, and also from the anodes and other portions of the rectifier; These heating elements may be supplied from a transformer 16 byway of connections 17, the energization of the heating elements being controlled by a switch 18, and the heating elements associated with different anodes being shown connected by lead 19. Effective results are obtained by maintaining the heating elements at a temperature of 500 to 800 Centigrade. It is advantageous if'heating of the anode spaces is effected before the operating current is impressed on the rectifier itself, and to permit this the transformer 16 may be a special transformer, which may be disconnected if sufficient heating effect can be supplied to the heating elements by the rectifier arc itself.

The example illustrated in Fig. 2 differs from that shown in Fig. 1 in having the heat ing coils 15' disposed outside the anodeshields 14, but separated from the rest ofthe vacuum space by additionaljshields 20. The anode space is thus heated indirectly through the medium of the intervening shield, which shield may be equipped with various other heating elements arranged to derive their heat from the arc and maintain the heat in the enclosed space. The other figures illustrate various arrangements of heating elements which derive their heat from the are. A generalrequirement of such heating elements is that they be of such material and so arranged as tobe heated by the are to. such a degree that they are enabled to maintain the anode space at the desired temperature during the period in which the anode is carrying no current. In general, this energy can be obtained from. the arc'onl'y at the priceof a considerablevoltage drop, but' by suitably designing such heating elements, excessive voltage drops may be ass sts avoided. When these elements are made of metal and are heated by the rectifier current only, they should be capable of being brought to a dull red heat in a very short time, but must not fuse under the highest overloads. Consequently, they should preferably be constructed of some heat-resisting, non-friable metal such as tungsten, tantalum, molybdenum or iridium; however. iron or chrome nickel, which are" not attacke'dby mercury, may also be used. f 7

Such arrangement is shownin connection withan'ode 12 in the rectifier illustrated in Fig. 3, and inthe horizontal section of the anode 1 2 in Fig. 4. Itcomprises a plurality of parallel vertically disposed metal rods 21 supported on the shield 1 f by slender spiders 22 extending from a central thickerrod 23. These rods are heated bythe discharge current passing between the anode and the cathode and are constructed so as tob'e maintained at a dull red heat, and'be able to heat the gas and vapor in the space within the shield 14. In the arrangement associated with the anode 12 in Fig. 3," the anode shield-14 of metal is especially equipped to function' as' aheating element by having its outer surface highly polished and its inner surface roughened or formed with projections in the nature of heating elements, as designated z t-14. Nhile it is of importance to have the anode shields well heat insulated from the casing in all instances, it is of particular importance with this form of heating device. This form anode shield heater is of special advantage, because it avoids increase in the voltage-drop across the forwarder rectified current are to a greater extent than the other forms.

As seen in the drawing, the shields -surrounding the anodes are' made in the form of relatively long tubular members. The anodes with the shields are disposed on the sides of the rectifier tank, the'shields having openings at the bottom at adistance below the anodes. The shield openings lie outside the space above the Cathode area so as-to prevent the mercury blast from the cathode from entering into the shields. Theheating elements for superheating the anode region are disposed adjacent tothe anode surfaces and are-"so positioned as to interfere as little as possible with the play of the are through the anode shield openings. In all of the arrangements,

the anode shields occupy only a small part 'of the heating members within theinterior of the'total cross sectional area of'the tubular spacewithin'theshield so that the arc is free to play throughthe relatively large area tubu' ,lar spaces formed between the heating 'members. The mouth of the shield is in all cases left free, the heating members terminating at a distance back of the shield opening. In all of the arrangements the cross-sectional "area within the shields'occupied by the heating members ,islesstha-n one-half of the opening at the mouth of the shield through which the are passes.

It will be understood that in the foregoing illustrations and descriptions, reference has been omitted to many of the well-known fea-- tures of the rectifier itself, the disclosures herein being principally concerned with the novel heating arrangement and novel method 'of operation of the rectifier which involves the heating or maintenance of the temperature of the spaces about the anodes during their periods of inactivity, as Well as during their active periods, for the purpose of effecting a reduction of the vapor density and gas density in those regions. This is effective to reduce the possibility of reverse arcing to an inactive anode.

What I claim is:

1. In a vapor rectifier comprising a herm'etically closed evacuated vessel, a cathode and a plurality of anodes insulatingly mounted within said vessel and adapted to develop vapor during operation, tubular shields surrounding said anodes arranged to divert the stream of vapor from said anodes, each of said shields having an opening for passing the arc therethrough, and electrical heater elements within said shields in front of said anodes at a point back of said opening proportioned to be heated during operation by electric current to a temperature of the on der of 500 degrees Centigrade or more for reducing the gas density in the space adjacent to said anodes. V

2. In a vapor rectifier comprising a hermetically closed evacuated vessel, a vaporiza ble cathode and a plurality of anodes insulatingly mounted within said vessel, tubular shields surrounding said anodes arranged to divert the stream of vapor from said anodes, each of said shields having an opening for passing the arc therethrough, and electrical heater elements exposed within said shields in front of said anodes at a point back of said opening and proportioned to be heated during operation by electric current to a temperature of the order of 500 degrees centigrade or more for reducing the gas density in the space adjacent to said anodes, said heater elements occupying a relatively small part of the cross-sectional area of the tubular space within said shields.

3. In a mercury-vapor rectifier, a hermetically closed evacuated vessel, an insulated cathode at the bottom of said vessel, a plurality of anodes at the top of said vessel, said anodes acting alternately as valves preventing current flow while the potential applied to said anodes is negative, and permitting current flow in the intermediateperiods when they are at positive potential, tubular metallic shields individually enclosing said anodes, said shields having openings at the lower ends thereof ata distance from said anodes so arranged as to cause the vapor from said cathode to be diverted from said anodes, and electrical heater elements disposed inside said shieldsin front of the anodes and proportioned to be heated during operation by electric current to a temperature of the order of 50.0: degrees centi grade or more, said heating means being so arranged "as to leave unobstructed at least one-half of the total crosssectional area of the tubular space within said shields. I a P 4:. Ina mercury-vapor rectifier, a hermetically closedi evacuated vessel, an insulated cathodezat the bottom of said vessel,a plurality ofanodes at the top' of said vessel, said anodes acting alternately as valves preventing current flow: whilethe potential applied to said anodes is negative, and permitting cur rent flow in the intermediate periods when they are at positive potential, tubular metallic shields individually enclosing said anodes,saidishields having openings at the low er ends thereof at a distance from said anodes so arranged as to causethe vapor'from said cathode to be diverted from said anodes, and electrical heater elementsdisposed inside said shields between the anodes and shield openings, and proportioned to be heated during operation by electric current to a temperatureof the order of 500 degrees Centigrade or more, said-heater elements leaving entirely unobstructed the openings of said anode shields and-leaving unobstructed at least onehalf of thetotal cross-sectional area of the tubular space within said shields.

' 5. In a mercury-vapor rectifier, a hermetically closed evacuated: vessel, an insulated cathode atthe bottom of said vessel, a plurality of anodes at the top of said vessel, said anodes acting alternately as valves preventing current flow while the potential applied to said anodes is negative, and permitting current flow in'the intermediate periods-when they are at positive potential, tubular metallic shields individuallv enclosing said'anodes, said shields having openings at the lower ends thereof at a distance from said anodesso arranged as to cause the vapor fromsaidcath-- ode to be diverted from said anodes, andelect-ric'alv heater elements within said anode shields in front of said anodes and proportioned to be heated during operation by electric current to a temperature of the order of 500 degrees centigrade or more, said heating means extending for a substantial length in the direction of the shields and terminating at a distance back of said anode openings leaving substantially unobstructed the entire cross sectional area of said openings.

6. Avapor discharge device comprising a gas tight vessel containing vapor, a cathode, an anode for maintaining a discharge with said cathode through said vapor, a tubular sleeve surrounding said anode and confining a portion of the discharge path in front of said anode, and electrical heater elements exposed to the space within said'shield in front of said anode and proportioned to be heated during operation by electric current to a temperature of the order of'500 degrees centigrade or more.

7. A'vapor discharge device comprising a gas tight vessel containing vapor, a cathode, an anode for maintaining a discharge with said cathode through said vapor, a tubular Y sleeve surrounding said anode and confining a portion of the discharge path in front of said anode, and electrical heater elements supported by said sleeve in front of said anode for reducing the vapor density in said space, said heater elements leaving substantially unobstructed the tubular dischargepath through said sleeve and proportioned to be heated by electric current during operation to a temperature of the order of 500 degrees centigrade or more. i

Y 8. A vapor-discharge device comprising a gas tight vessel containing vapor, a cathode, an anode for maintaining a discharge With said cathode through said vapor, a-shield surrounding said anode and' confining aportion ofthe discharge path in frontof said anode, and electrical heater elements associatedwith said shield in front of said anode and proportioned to be heated during operation by electric current to a temperature of the order of 500 degrees Centigrade or above for reducing the vapor density within said shield.

9. A vapor-discharge device comprising a gas tight vessel containing vapor, a cathode, a plurality of anodes for maintaining a discharge with said cathode through said vapor, a plurality of shields surrounding said anodes and confiningv a portion of the discharge path in front of said anodes,- and electrical heater elements exposed to the spaces within said shields in front ofsaid anodes and proportioned to be heated during. operation by electric current to a temperature of the order of 500 degrees centigrade or above for reducing the vapor density within said shields.

In testimony whereof I have hereunto sub scribed my name-this-13 day of January, A. D. 1928-, at Zurich, Switzerland.

ARTHUR- GAUDENZI. 

